The broad, long-term objective of this proposal is to elucidate some of the structure-function relationships of reverse transcriptase (RT) from Human Immunodeficiency Virus (HIV), the etiological agent of AIDS. The specific aims leading toward this long-term objective are to: 1) identify the stoichiometry of the active form of HIV RT, 2) investigate and characterize the protein-protein interactions of the HIV RT subunits, and 3) identify the region of HIV RT which is directly involved in primer-template recognition. AIDS is a significant public health problem both nationally and world-wide. HIV reverse transcriptase is one of several virally-encoded proteins required for viral replication, and as such continues to be the focus for chemotherapy. The results of this investigation are expected to provide information which will assist rational drug design efforts for specific inhibitors of HIV RT. The methodology involves using cloned HIV RT subunits expressed in yeast and E. coli. Proposed experiment combine chemical modification to detect essential residues with site-directed mutagenesis and/or deletion mutations to locate regions of primary and secondary structure which are required for the functions of protein-protein interactions and primer-template binding.